The present invention relates to processing of bulk materials. More particularly, the present invention relates to separation of liquids from bulk materials and to a screw press arrangement for separating liquids from bulk materials such as livestock manure.
Numerous industries utilize compression devices such as screw press liquid separators to remove liquid from bulk materials such as wood chips, livestock manure, byproducts of food processing operations, or other fibrous materials. The screw press liquid separators are based on the principle of a screw rotating inside a cylindrical or conical cage that forces the bulk material from the inlet of the screw to an output in a manner that compresses the bulk material. The cage can be equipped with holes, usually conically drilled, or slots or bars arranged in such a fashion as to provide for drainage of the liquid that is squeezed from the bulk material.
The various uses of screw press liquid separators involve a number of mechanisms for creating pressure between the chamber and the shaft bearing flights. The inner diameter of the chamber may be cylindrical, conical, or may contain restricted areas. All of these features together with variations in the diameter of the shaft or diameters of the flutes on the shaft can produce changes in the pressure exerted on the wood chips or other material being treated in the screw press liquid separator. The chamber of the plug screw feeder may be comprised of bars, screens or be solid depending upon whether the screw press liquid separator is being used to drive off excess water from materials such as livestock manure or being used to refine materials such as wood chips or both remove excess fluid and refine. In various applications the pressure and throughput is controlled by the voids if any in the chamber, the restrictions in the chamber, the shaping of the shaft or flutes and the torque applied to the screw feeder. Numerous examples of screw press liquid separators are known in the art.
U.S. Pat. No. 5,515,776 discloses a worm screw press having drainage perforations in the press jacket. The size of the shaft for the worm screw increases in cross-sectional area in the flow direction of the drained liquid.
U.S. Pat. No. 7,357,074 is directed to a screw press with a conical dewatering housing with a plurality of perforations for the drainage of water from bulk solids compressed in the press. A perforated casing or jacket is used.
U.S. Pat. No. 3,394,649 discloses a worm press used for the dewatering of sludges or cellulose pulp suspensions and comprises a hollow worm shaft having apertures at the end of the pressure zone. Through these bores still further liquid can be drained into the hollow shaft, this liquid draining inside the shaft in a direction opposite to the conveyance direction.
These prior-art worm screw configurations appear to operate for their intended purposes, but require the use of tapering screws, screw jackets or both, or require hollow shafts with provision for drainage. All of these features complicate their construction.
Therefore, there is a need for a new screw press arrangement for separating liquids from bulk materials which is not associated with these disadvantages.